Fuel delivery systems may include a direct fuel injector to inject fuel at high pressure directly into a cylinder. Highly pressurized fuel in the fuel delivery system may be particularly useful during crank and other times during engine operation for efficient combustion, etc. The direct fuel injector may deliver fuel in proportion to a fuel injector pulse width of a signal from an engine controller. However, due to aging, fuel contamination, or hardware failure, undesired fuel outflow from one or more fuel injectors may occur. Undesired fuel outflow from the fuel injector may cause the corresponding cylinder receiving fuel from the injector to misfire. Consequently, non-combusted air-fuel mixture may be displaced into the exhaust. The non-combusted air-fuel mixture in the exhaust may participate in an exothermic reaction at an exhaust catalyst generating excess amounts of heat. The heat generated may cause excessive increase in exhaust temperatures, which may result in thermal degradation of the exhaust components.
In some cases, depending on the amount of undesired fuel outflow from the fuel injector(s), an onboard control strategy may be able to correct for the undesired fuel outflow from the fuel injector(s) by leaning out the air/fuel ratio. However, while this corrective action can take place during conditions of engine operation, in other conditions correcting for undesired fuel outflow from the fuel injector(s) by leaning out the air/fuel ratio may not be possible. For example, during an idle stop or at key off, or in the example of a hybrid electric vehicle (HEV) driven in battery mode, undesired fuel outflow from the one or more fuel injector(s) may continue to add fuel into the one or more respective cylinder(s). The undesired outflow of fuel from one or more fuel injector(s) under circumstances wherein corrective action such as leaning out the air/fuel ratio is not possible can lead to potential issues including but not limited to hesitation/stumbles in the engine at startup, engine hydrolock, fuel smell in the vehicle cabin, increased emissions, etc. For example, depending on the position of the intake and exhaust valves at engine shutoff, unburned hydrocarbons inside the cylinder(s) may migrate to the intake or exhaust manifolds and escape to the atmosphere, resulting in increased evaporative emissions.
One example approach for mitigating undesired fuel outflow from a fuel injector is shown by Wakemen et al. in U.S. Pat. No. 5,685,268. Therein, in response to detecting leakage in the fuel delivery system, the engine may be operated in a limp-home mode at reduced fuel pressure.
However, the inventors herein have identified potential issues with such an approach. As an example, reducing fuel rail pressure alone may not prevent undesired fuel outflow from the fuel delivery system, therefore potential issues such as engine hydrolock, fuel smell in the vehicle cabin, increased emissions, etc., may not be mitigated.
In one example approach for mitigating the emission of hydrocarbon vapor to the atmosphere, U.S. Pat. No. 6,581,580 B2 teaches a vapor evacuation system that is used to intermittently remove hydrocarbon vapors from vehicle components to an available storage canister using an electrically-controlled pump.
However, the inventors herein have also recognized that such an approach may not be sufficient for reducing evaporative emissions responsive to undesired outflow of fuel from one or more fuel injectors, depending on the position of the intake and exhaust valves at engine shutoff. For example, if a cylinder is positioned with an intake valve closed and an exhaust valve open at engine shut-off, a pump may not be capable of evacuating fuel vapors to a vapor storage container, and increased evaporative emissions may result.
Thus, the inventors herein have developed systems and methods to at least partially address the above issues. In one example the issues described above may be addressed by a method including, monitoring a plurality of fuel injectors that each supply pressurized fuel to a plurality of cylinders in a combustion engine, and responsive to an indication of a fuel injector with undesired fuel outflow, following an engine-off event, positioning a cylinder that receives fuel from the fuel injector with an intake valve open and an exhaust valve closed, coupling the cylinder to a fuel vapor canister configured to store vaporized hydrocarbons, and activating a vacuum pump to purge fuel vapors resulting from the undesired fuel outflow through the intake valve to the fuel vapor canister.
As one example, positioning a cylinder that receives fuel from the fuel injector with an intake valve open and an exhaust valve closed includes spinning a vehicle engine unfueled with an onboard electric motor responsive to an engine-off event. In this way, upon detecting undesired fuel outflow from a fuel injector, at an engine-off event, the cylinder that receives fuel from the fuel injector with undesired fuel outflow may rapidly be configured with its intake valve open and exhaust valve closed, wherein a pump may subsequently be activated to purge fuel vapor in the cylinder to a fuel vapor canister, thereby reducing the potential for undesired evaporative emissions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.